You're presuming that. Romo doesn't have a big arm and has never been a huge threat deep. However, keep in mind that passes of 40 yards (air length) are unusual in the NFL. There were only 351 passes of same in 2014. That averages to 10.4 passes per YEAR per team.
If you use the 'normal' 20 yard pass (remember a 15 yd out may be from a 30 yard in the air pass) then you get a compromise. The best IMO is Rodgers. Another is Romo although his YPA is about 14 but his INT% is the lowest in the NFL over the last 3+ years. He's only thrown a tad over 100 'long balls' in the period of 2013-14. Avg attempts over that period was about 130.
You'll have to define your position as this topic is hard to discuss otherwise and is still always going to be a narrative in the end.
Romo will hopefully be back for most if not the full season, but this is not guaranteed and his top 5 status will become vulnerable due to proven back problems that tend to worsen over time; not improve. This was on full display in the past with Aikman back problems forcing him to be
released due to inadequate play; aka Aikman redux = not one other team would sign Aikman even while still wanting to play. His retiring a Cowboy is a nice revision of history that seems to get a pass due to ignorance of younger fans acceptance of the narrative.
Draft a QB high to avoid the tried and failed short term fixes of when/if Romo goes down or shows declining play either due to age or back problems. When you draft 4 overall and have a QB who is 36, it makes sense to take a top QB prospect in general as they are not likely to come fro latter rounds. On top of this, last season proved the organization and coaching (JG/Linehan/Wilson mainly) can't evaluate QB talent properly and why Weeden failed and a future draft pick was thrown away on Cassel in desperation. The lack of QB evaluation talent on this team lead to a 4-12 season mainly due to a QB who is able to hid for coaching/scheme/talent deficiencies = 1 win w/out Romo in '15.
This puts the burden of the franchise to think long term with their QB situation and maintaining the "brand" if Romo goes down long term.